Osteoarthritis (OA) is the most common form of arthritis in the United States, affecting 21 million older people. Knee OA in the elderly is one of the most frequent causes of loss of independence and physical disability. There are currently no satisfactory pharmacological or non-pharmacological therapies for knee OA. New strategies to improve functional capacity, quality of life and reduce long-term disability in people with knee OA are urgently needed. Our long-term goal is to demonstrate the physical and psychological benefits of Tai Chi exercise as a complementary treatment for people with knee OA. Tai Chi is a traditional Chinese discipline with both physical and mental components that appear to benefit a variety of conditions. The physical component provides exercise that is consistent with recommendations for OA (range of motion, flexibility, muscle conditioning and aerobic cardiovascular exercise), while the mental component has the potential to increase psychological well-being, life satisfaction, and perceptions of health. These effects are especially pertinent for the treatment of older adults with knee OA. In a pilot study of Tai Chi in patients with Rheumatoid Arthritis that we completed in 2003, 50% of the patients were randomized to the Tai Chi group and achieved improvement in our primary outcome (American College Rheumatology 20 response criteria) compared with 0% in our attention control. Because of the immense impact that knee OA has on the elderly in the US, we propose to conduct the first pilot randomized controlled trial of Tai Chi in OA. Over a three year period, 40 patients with knee OA (20 randomized to Tai Chi and 20 to an attention control intervention) will be compared in a 12-week program and at 3 and 6 month follow up. Our aims are (1) to determine the feasibility and logistics of conducting a randomized controlled trial of Tai Chi in patients with knee OA; (2) to study effects on pain relief (as a marker of disease activity), function and functional independence (a marker of impairment), disability and health status in elderly people with knee OA. This proposed pilot study will provide preliminary data on the potential acceptability and safety of Tai Chi for knee OA and will be used to inform future large-scale studies to determine the efficacy of this alternative therapy.